The present invention relates to a liquid crystal display, and more specifically to an optically compensated birefringence liquid crystal display.
Liquid crystal displays are widely used in various applications due to low power consumption and lightweight for mobile.
Unfortunately, there are some drawbacks, for example, contrast ratio may be deteriorated by the increased viewing angle, thus, extension of viewing angle is limited. Compared to CRT displays, Liquid crystal displays have slower response speed, resulting in image delay. The National Television Standard Committee (NTSC) dictates that a video frequency signal must be shown once within a 16.7 ms period. Currently, response speed between white and black displays is adequate. Response speed for multiple gray levels is slow, however, particularly for regions having a lower effective applied voltage difference. Thus, a liquid crystal display with wide viewing angle and high response speed is desirable.
To solve the problems, an optically compensated birefringence (OCB) liquid crystal display has been developed. FIG. 1 depicts a cross-section of a conventional optically compensated birefringence (OCB) liquid crystal display 10. The liquid crystal display 10 includes an upper substrate 20 having an upper electrode 22 and an upper alignment layer 24 formed thereon in order, a lower substrate 50 having a lower electrode 52 and a lower alignment layer 54 formed thereon in order, and a liquid crystal layer 40 comprising a plurality of liquid crystals 42 installed between the upper and lower substrates. Referring to FIGS. 2a-2c, liquid crystal arrangements of the optically compensated birefringence (OCB) liquid crystal display 10 with various applied voltages are illustrated. The liquid crystal layer 40 comprises a first liquid crystal region A contacting with the upper alignment layer 24, a third liquid crystal region C contacting with the lower alignment layer 54, and a second liquid crystal region B installed therebetween.
Referring to FIG. 2a, the liquid crystals 42 in the first and third liquid crystal regions (A and C) have small included angles with the upper and lower alignment layers (24 and 54), respectively, at the initial state of zero applied voltage, and the liquid crystals 42 in the second liquid crystal region B are almost parallel to the alignment layer. These liquid crystals present a splay state arrangement.
Referring to FIG. 2b, the liquid crystals 42 in the first and third liquid crystal regions (A and C) have small included angles with the upper and lower alignment layers (24 and 54), respectively, with an increased applied voltage from zero to a critical voltage (Vc), and only the central liquid crystal 42 in the second liquid crystal region B is perpendicular to the alignment layer. These liquid crystals present a bend state arrangement, which is a bright state of an optically compensated birefringence (OCB) liquid crystal display.
Referring to FIG. 2C, the liquid crystals 42 in the second liquid crystal region B are almost perpendicular to the alignment layer, with an increased applied voltage from the critical voltage (Vc) to a Vd voltage (more greater than Vc), which is a dark state of an optically compensated birefringence (OCB) liquid crystal display. The optically compensated birefringence (OCB) liquid crystal display provides high response speed and wide viewing angle due to the regular arrangement of the liquid crystals cooperated with OCB special optical film.
The operating voltage of an optically compensated birefringence (OCB) liquid crystal display ranges from Vc (critical voltage) to Vd. A high voltage (usually, more than 20V) converts the splay state to the bend state, that is to say that the extra driving system needs to use in OCB. As shown in FIG. 3, correct retardation (Δ nd) and compensated film are very important in OCB panel.